Pharmacokinetics, sometimes abbreviated as PK, is a branch of pharmacology dedicated to determining the fate of substances administered to a living organism. The substances of interest include any chemical xenobiotic such as, pharmaceutical drugs, pesticides, food additives, cosmetic ingredients, etc. It attempts to analyze chemical metabolism and to discover the fate of a chemical from the moment that it is administered up to the point at which it is eliminated from the body. Pharmacokinetics is the study of how an organism affects a drug, both together influence dosing, benefit, and adverse effects, as seen in PK/PD models. Pharmacokinetic properties of chemicals are affected by the route of administration and these may affect the absorption rate. Models have been developed to simplify conceptualization of the processes that take place in the interaction between an organism and a chemical substance. The various compartments that the model is divided into are commonly referred to as the ADME scheme, absorption - the process of a substance entering the blood circulation. Distribution - the dispersion or dissemination of substances throughout the fluids, metabolism – the recognition by the organism that a foreign substance is present and the irreversible transformation of parent compounds into daughter metabolites. Excretion - the removal of the substances from the body, in rare cases, some drugs irreversibly accumulate in body tissue. The two phases of metabolism and excretion can also be grouped together under the title elimination, the study of these distinct phases involves the use and manipulation of basic concepts in order to understand the process dynamics. All these concepts can be represented through mathematical formulas that have a graphical representation. The model outputs for a drug can be used in industry or in the application of pharmacokinetic concepts. Clinical pharmacokinetics provides many performance guidelines for effective and efficient use of drugs for human-health professionals, in practice, it is generally considered that steady state is reached when a time of 4 to 5 times the half-life for a drug after regular dosing is started. Noncompartmental methods estimate the exposure to a drug by estimating the area under the curve of a concentration-time graph, compartmental methods estimate the concentration-time graph using kinetic models. Noncompartmental methods are more versatile in that they do not assume any specific compartmental model. The final outcome of the transformations that a drug undergoes in an organism, a number of functional models have been developed in order to simplify the study of pharmacokinetics. These models are based on a consideration of an organism as a number of related compartments, the simplest idea is to think of an organism as only one homogenous compartment. However, these models do not always reflect the real situation within an organism
Graph that demonstrates the Michaelis–Menten kinetics model for the relationship between an enzyme and a substrate: one of the parameters studies in pharmacokinetics, where the substrate is a pharmaceutical drug.
Different forms of tablets, which will have different pharmacokinetic behaviours after their administration.
The time course of drug plasma concentrations over 96 hours following oral administrations every 24 hours. Note that the AUC in steady state equals AUC∞ after the first dose.
Graph representing the monocompartmental action model.